Hydrostatic drive control device

ABSTRACT

A device for controlling a hydrostatic drive (1) having a resonator (2) which is connected on the one hand to the hydrostatic drive (1) and on the other hand to a pressurized-fluid supply line (4) and to a return line (5), and having a periodically actuatable switch valve (3) which connects the resonator (2) alternately with the pressurized-fluid supply line (4) and the return line (5). In order to assure advantageous control conditions, the resonator (2) has at least one pressure chamber (6) with a movable, oscillatable chamber limitation (7) for changing the chamber volume movable chamber limitation (7) form a part of a single-mass oscillator comprising mass and spring (10). The pressure chamber (6) which can be connected alternately with the pressurized-fluid supply line (4), the return line (5) and the hydrostatic drive (1) can be acted on via the switch valve (3) with a switch frequency which lies in the supraresonance region of the single-mass oscillator.

FIELD AND BACKGROUND OF THE INVENTION

The present invention refers to a device for controlling a hydrostaticdrive having a resonator which is connected on the one hand to thehydrostatic drive and, on the other hand, to a pressurized-fluid supplyline and a return line, and having a periodically actuatable switchvalve which connects the resonator alternately with thepressurized-fluid supply line and the return line.

In order to avoid, in particular, the throttle losses ofthrottle-controlled hydrostatic drives, it is known not to connect thedrive continuously via a throttle valve but rather periodically to ahydraulic-fluid supply line or a return line over switch valves eachconnected in parallel with a non-return valve. The opening of the switchvalve in the hydraulic-fluid supply line results in an accelerating ofthe drive, the inertia of which upon the closing of this switch valveleads to a reduction in the pressure of the compressible hydraulic fluidin the drive region to a pressure which is less than the closurepressure of the non-return valve in the region of the return line sothat, via the return line, hydraulic fluid can be drawn in until theswitch valve in the supply line again opens and the process is repeated.In the event of a useful braking of the drive there results, upon theclosing of the switch valve in the return line, an increase in thepressure of the drive-side hydraulic fluid to an amount exceeding theclosing pressure of the non-return valve in the region of the supplyline, which brings about a pumping of the hydraulic fluid back into thesupply line. This additional flow of hydraulic fluid made possible bythe pulsating control of the drive brings about a corresponding recoveryof energy and thus an improved efficiency which, to be sure, ispurchased at the cost of a comparatively slight dynamism and acorresponding structural expense.

In order to adjust the operating pressure for the hydrostatic driveindependently of its operating path between the maximum pressure offeredby the hydraulic-fluid supply line and the pressure of the return line,it has already been suggested that the hydrostatic drive be connected toa resonance tube which is connected alternately via a periodicallyactuatable switch valve to a pressurized-fluid supply line and a returnline in order to produce standing pressure waves of the hydraulic fluidin the resonance tube under conditions of resonance. By the provision ofa pressure outlet in an oscillation node of the resulting standingpressure waves in the resonance tube, it is possible to provide at thispressure outlet an operating pressure for the drive via the operatingpath of the drive. Furthermore, the pressure waves of the arrangementsassociated with this node at the pressure outlet are suppressed so that,despite a pulsating control, the pulsation in time of the operatingpressure at the pressure outlet is comparatively slight. Since thelength of the resonance tube must be selected as a function of thelength of the pressure waves formed in the hydraulic fluid,corresponding tube lengths are to be expected which may limit thepossible use of these devices. Furthermore, due to the pressureadjustment, such a device is advisable for the adjustment of thepressure, in particular for the acceleration control.

SUMMARY OR THE INVENTION

The object of the invention is therefore so to develop a device forcontrolling hydrostatic drives of the type described above that the useof a resonance tube is unnecessary and speeds can preferably becontrolled.

According to the invention achieves the task in view in the manner theresonator has at least one pressure chamber having a movable,oscillatable chamber delimitation for changing the volume of thechamber, the movable chamber limitation forms a part of a single-massoscillator comprising of mass and spring, and the pressure chamber whichcan be connected alternately with the pressurized-fluid supply line, thereturn line and the hydrostatic drive can be acted on via the switchvalve with a switch frequency which lies within the supraresonanceregion of the single-mass oscillator.

By the pressure chamber of variable volume in combination with thesingle-mass oscillator, the result is obtained that the pressurizedfluid which flows during the connection of the pressure chamber on theone hand with the pressurized-fluid supply line and, on the other hand,with the return line into the pressure chamber, during the connection ofthe pressure chamber with the hydrostatic drive is forced again out ofthe pressure chamber, as a result of the energy stored in the spring ofthe single-mass oscillator, so that a volumetric flow of the hydraulicpressurized fluid which is dependent on the switch frequency of theswitch valve is established, which therefore also can be controlled inadvantageous manner via the switch frequency of the switch valve. Forthis purpose, to be sure, there can only be meaningfully used switchfrequencies in the supraresonance region of the single-mass oscillatorand therefore in a frequency range above its resonance frequency. Due tothe simple possibility of influencing the volumetric flow, the device isin particular suitable for speed control.

Since the volumetric flow of the hydraulic pressurized fluid for thehydrostatic drive also depends on the open time of the switch valve forthe connection of the pressure chamber with the pressurized-fluid supplyline, this open time can be set for the control of the volumetric flow.Use is made of this possibility in particular when, with comparativelysmall volumetric flows, the switch frequency can no longer be increaseddue to the existing structural conditions. The efficiency of the controldevice of the invention depends on the friction occurring in the regionof the single-mass oscillator, the liquid friction and the pressurelosses in the region of the switch valve and can be influenced by theopen time of the switch valve, particularly when the volumetric flow iscontrolled via the switch frequency. It has been found that for afavorable efficiency, the open time of the switch valve for thepressurized-fluid supply line must be changed proportionately to thepressure in the connecting line of the drive.

Another possibility of adjustment results from the selection of the opentimes for the connecting line of the hydrostatic drive. If, namely, theconnected time of the drive to the pressure chamber is correspondinglyshortened as compared with the connected time to the pressurized-fluidsupply line and to the return line, then a hydraulic average pressurewhich exceeds the pressure in the pressurized-fluid supply line can bemade available for the drive. Upon an increase of the connected times ofthe drive for the connection to the pressure chamber, the volumetricflow can, on the other hand, be decreased, with the advantage that theefficiency is not impaired, contrary to a volumetric-flow control viathe open time of the pressurized-fluid supply line.

If the volumetric-flow variations or the pressure variations are to bereduced on the connection side of the hydrostatic drive, then theconnecting line between the pressure chamber and the hydrostatic drivecan be connected with a pressure storage which sees to a correspondingcompensation of the pressure variations.

The pressure chamber can be developed in various ways since the onlyimportant thing essentially is an oscillatable chamber limitation whichchanges the chamber volume. For this purpose, the pressure chamber ofthe resonator can consist of a cylinder the piston of which whichproduces the movable chamber limitation forms the single-mass oscillatorwith at least one spring acting on the piston. This cylinder may beacted on only from one side by the hydraulic pressurized fluid.Particularly advantageous conditions result to be sure when theresonator is developed as a cylinder which can be acted on on bothsides, its two pressure chambers being connected with respect to theirswitch periods by switch valves which are 180° out of phase, eachindividually to a pressurized-fluid supply line one the one side and thereturn line as well as, on the other hand, to a hydrostatic drive, sincein this case the action on the piston on the one side can be used forthe ejection of pressurized fluid on the other side. In this connection,the connecting lines for the hydrostatic drive on the two sides of thecylinder need not be necessarily connected to a common hydrostaticdrive.

Another embodiment for the pressure chamber of the resonator is obtainedif the movable chamber limitation of the pressure chamber consists of abellows or a membrane. In combination with a spring-loaded mass, asimple single-mass oscillator can also be prepared for such a pressurechamber, in which case similar manners of action are established.

The producing of dependable switch connections between the pressurechamber on the one side and the hydrostatic drive as well as thepressurized-fluid supply line or the return line on the other hand inthe required switch frequency represents an essential condition for thepractical use of a control device in accordance with the invention. Inorder to satisfy such structural requirements, the switch valve can bedeveloped as rotary piston valve with a rotary piston, which alternatelyconnects the pressure chamber or pressure chambers via control portswith connecting chambers which are connected to the pressurized-fluidsupply line, the return line or the connecting line for the hydrostaticdrive. During a revolution of the piston, the connections of thecorresponding pressure chambers are connected one after the other to thecorresponding lines, in which connection the control ports assure arapid opening and closing of these connections. The provision of arotary piston offers in addition to this the advantage of being able toarrange several pressure chambers distributed uniformly over thecircumference. The pressure chambers can in this connection becontrolled axially as well as radially, in the same way as the axes ofoscillation of the single-mass oscillators of the pressure chambers canextend radially or paraxially to the piston of rotation. Radial axes ofoscillation of the single-mass oscillators to be sure permit a completeequalization of mass in the event of a corresponding arrangement.Paraxial axes of oscillation to be sure offer structural advantages forresonators which can be acted on on the sides.

In order to control the switch times of a rotary piston valve theswitching frequency of which depends on the speed of rotation of thepiston, there can be arranged, coaxial to the rotary piston, controlbodies which are rotatably displaceable with respect to the pressurechamber or the pressure chambers which are arranged with rotationalsymmetry with respect to the rotary piston, preferably in the form ofcontrol disks or sleeves, which control bodies form control edges whichcooperate with the control ports of the rotary piston. By these controledges, the control ports of the rotary piston are released or closed sothat the switch times of the switch valve can be adjusted via therotational position of the control bodies forming the control edges.Control disks cooperate in this connection via radially aligned controledges with end control ports of the rotary piston while the controlsleeves have axially directed control edges for control ports providedin the piston wall. By a suitable combination of such control disks orsleeves, the individual switch times of the switch valves canaccordingly be adjusted in accordance with the specific requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

With the above and other objects and advantages in view, the presentinvention will become more clearly understood in connection with thedetailed description of preferred embodiments, when considered with theaccompanying drawings of which

FIG. 1 shows a device in accordance with the invention for controlling ahydrostatic drive in the form of a simple block diagram;

FIG. 2 shows a time diagram of the switch positions of a switch valve ina coordinate system on the ordinates of which the three switch positionsare plotted and on the abscissae of which the switch times referred tothe duration of the period are plotted;

FIG. 3 shows the dependence of the average volumetric flow through theresonator, referred to a rated flow, on the switch frequency of theswitch valve referred to the resonance frequency and of the open time,referred to the pressurized-fluid supply line referred to the switchperiod in a three-dimensional coordinate system;

FIGS. 4 and 5 show the mutual dependence of the average volumetric flowthrough the resonator of the open time, referred to the switch period,of the connection for the hydrostatic drive and of the pressure in theconnecting line, referred to the pressure in the supply line, for thehydrostatic drive, in a three-dimensional coordinate system;

FIG. 6 is a block diagram of a device in accordance with the inventionwhich is amplified as compared with FIG. 1;

FIG. 7 shows a further embodiment of a resonator in a simplified axialsection.

FIG. 8 shows a simplified axial section through a switch valve;

FIG. 9 is a section along the line IX--IX of FIG. 8;

FIG. 10 is a section along the line X--X of FIG. 8; and

FIG. 11 is a section along the line XI--XI of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The device for controlling the hydrostatic drive 1 of, for instance, aworking cylinder, has, in accordance with FIG. 1, a resonator 2 which isconnected alternately by means of a periodically actuatable switch valve3 with a pressurized-fluid supply line 4, with a return line 5 to apossibly prestressed hydraulic-fluid tank and with the hydrostaticdrive. The resonator 2 is formed by a pressure chamber 6 having amovable, swingable chamber limitation 7, namely by a cylinder 8 thepiston 9 of which is active with a spring 10 as single-mass oscillator,when the piston 9 is acted on in the resonance region of the single-massoscillator via the switch valve 3 which is connected with a suitabledrive 11. The hydraulic fluid which is conveyed during the switchconnection with the pressurized-fluid supply line 4 or the return line 5into the pressure chamber 6 is fed during the resonator connection withthe hydrostatic drive 1, due to the energy stored in the single-massoscillator upon the hydraulic piston action via the connection line 12to the hydrostatic drive 1, in which connection in order to dampen thepressure pulses a pressure accumulator 13 can be provided. Such a switchcycle is shown in FIG. 2. During the time t_(D), the switch valve 3(switch position D) connects the resonator 2 with the pressurized-fluidsupply line 4 in order then to establish the connection with the returnline 5 in the switch position R, namely in the time t_(R) in which, as aresult of the inertia of the single-mass oscillator, hydraulic fluid isdrawn from the return line 5 into the pressure chamber 6. In the nextswitch position A, the hydraulic fluid, during the time t_(A) whichcorresponds to half the period in FIG. 2, is forced via the piston 9 bythe spring 10 into the connecting line 12. The volumetric flow throughthe resonator 2 is thus dependent on the switch frequency f of theswitch valve 3 and the relative open time T_(D) of the pressurized-fluidsupply line 4 within a switch period. If the losses which have occurredare disregarded, a dependence shown in FIG. 3 then results between theaverage volumetric flow q referred to a rate of flow to thepressurized-fluid supply line 4, the switch frequency f referred to theresonance frequency of the resonator, and the relative open time t_(D)of the pressurized-fluid supply line 4, in which connection only thefrequency range over the resonance frequency of the resonator 2 can bemeaningfully utilized. From FIG. 3, which shows a three-dimensionalcoordinate system with the axes x for the relative average volumetricflow q, y for the relative open time t_(D), and z for the relativeswitch frequency f, it can be noted that a change in the switchfrequency can be utilized in order to control the volumetric flow q inthe region of larger volumetric flows. Only with small volumetric flows,for which excessively high switch frequencies result, should the opentime t_(D) be used as setting value for the control of the volumetricflow q. Upon control of the volumetric flow via the switch frequency f,the open time t_(D) can be set for an optimizing of the efficiency whichis to be taken into account after all in view of the unavoidablefriction and pressure losses. The open time t_(D) is for this purpose tobe selected proportional to the pressure available for the drive 1.

Of course, the open time t_(A) for the connecting line 12 need notcorrespond to half the period. If an open time t_(A) which is less thanhalf the period is selected, then a pressure exceeding the pressure inthe pressurized-fluid supply line 4 can be made ready for the drive 1.With longer open times t_(A), on the other hand, the volumetric flow canbe lowered without a loss in efficiency. FIGS. 4 and 5 show in each casethe relationships determined for optimal efficiency between the relativeopen time t_(A), the pressure p at the connection A referred to theconstant pressure in the pressurized-fluid supply line, and the relativevolumetric flow q, on the one hand, for open times t_(A) less than andon the other hand greater than half a period, in which connection ineach case the open times t_(A) are plotted on the x axis of athree-dimensional coordinate system, the relative pressure p on the yaxis and the volumetric flow q referred to a rated flow on the z axis.The losses which occur were taken into account in this connection by arelative damping factor of 5%. It can be noted from FIG. 4 that withshorter open times t_(A), the relative pressure p can be considerablyincreased. Upon a lengthening of the open times t_(A) to more than halfthe period, the volumetric flow q can again be controlled within theregion of small amounts in accordance with FIG. 5.

It need not be particularly emphasized that, in contradistinction to theworking operation shown in the drawing, in braking operation thevolumetric flow flows from drive 1 to the return line 5 or thepressurized-fluid supply line 4, which leads to a change in the switchsequence and the switch times. The fundamental control conditions,however, remain the same.

As can be noted from FIG. 6, two pressure chambers 6 which can be actedon in shifted phase are provided, in which connection preferably themass of the single-mass oscillator determined by the piston 9 which isprovided between these pressure chambers 8 has springs 10 on bothactuation sides. With such a construction, a switch valve 3 is of courseto be provided for both pressure chambers 6, which see to it that theswitch periods of the two switch valves are shifted in phase 180° fromeach other. In FIG. 2, the switch positions and times of the secondswitch valve which is driven with the same frequency but shifted inphase are indicated in dash-dot line.

The connections A of the two switch valves 3 are connected in accordancewith FIG. 6 with a common connecting line 12 for a hydrostatic drive,which, however, is not urgently necessary since separate drives can alsobe controlled via a common resonator.

The mass of the single-mass oscillator need not be formed by the piston9 of a cylinder, as is shown in FIG. 7, in which the pressure chambers 6are delimited by membranes 14 which connect the connecting flanges 15corresponding switch valves in liquid-tight manner with the oscillatormass and at the same time form the springs 10 of the single-massoscillator.

In order to be able to utilize the advantages of a resonator 2 inaccordance with the invention in order to control hydrostatic drives,suitable switch valves 3 for the required switch frequencies must beavailable. A device which satisfies these requirements and combinesseveral resonators with the corresponding switch valves is showndiagrammatically in FIGS. 8 to 11. It consists essentially of a housing18 containing a rotary piston 17 in which housing there are mountedopposite each other, in pairs, cylindrical holes 19 directed radially tothe rotary piston 17 having pistons 9 acted on by springs 10 whichrepresent single-mass oscillators in accordance with FIG. 1. Thepressure chambers 6 resulting on the inside of the pistons 9 areconnected via a control sleeve 20 surrounding the rotary piston 17 tothe rotary piston 17 which has control ports 21, 22 and 23, by means ofwhich the pressure chambers 6 can be alternately connected withconnecting chambers 24, 25 and 26 divided up in accordance with thearrangement of resonators for the pressurized-fluid supply line 4, thereturn line 5, and the connecting line 12. The connecting chambers 24,25 associated with the pressurized-fluid supply line 4 and the returnline 5 are provided in a control body 27 which is mounted rotatablydisplaceable within the hollow rotary piston 17. The connecting chambers25 associated with the connecting line 12 are, however, formed by aninsert 28 which is fastened in the housing and which passes coaxiallythrough the control body 27. In FIGS. 9 to 11, the switch position R isshown in which the pressure chambers 6 are connected with the returnline 5. In accordance with FIG. 10, this switch connection is obtainedvia the control ports 22 of the rotary piston 17 which are located inthe region of the connecting chambers 25 for the return line 5. Thecontrol ports 21 for the switch connection D which are present in theregion of the connecting chambers 24 for the pressurized-fluid supplyline 4 are covered, in accordance with FIG. 11, by a control ring 29which is fastened to the housing while the switch connection A, inaccordance with FIG. 9, is interrupted by the control sleeve 20. If therotary piston 17 which is driven via a shaft 30 turns continuously inthe direction of rotation of the arrow 31, then the switch connection Rvia the control ports 22 is interrupted by the control edges 32 of thecontrol sleeve 20, which at the same time opens the switch connection Avia the control ports 22 when the control ports 23 reach the controledges 33 of the control sleeve 20 which are shifted accordingly withrespect to the control edges 32 (FIG. 9). As can be noted from FIG. 11,the control ports 21 are still covered by the control sleeve 20 as longas the switch connection A is maintained. This switch connection A isonly interrupted when the control ports 23 come out of the region of theconnecting chambers 26. In this position of rotation of the rotarypiston, the switch connection D is released by the control edges 34 inaccordance with FIG. 11, until the control ports 21 leave the region ofthe corresponding connecting chambers 24, whereupon the switch cycledescribed is repeated.

In order to be able to adjust the switch times t_(D), t_(R) and t_(A),the control sleeve 20 and the control body 27 are displaceablerotatably, namely via drives which have not been shown in the drawing inorder not to clutter it. As can be noted from FIG. 9, the open timet_(A) for the switch connection A is determined by the position ofrotation of the control sleeve 20. The division of the switch timest_(D) and t_(R) over the remaining period results from the rotaryposition of the control body 27 with respect to the control sleeve 20.

In order that the control most favorable for the specific case of usecan be realized, it is advisable to provide a control such as indicatedin a block diagram in FIG. 1. The drive 11 for the switch valve 3 aswell as a setting device 35 for the control sleeve 20 and the controlbody 27 are controlled via a closed-loop control device 36 whichcontrols the switch frequency f, the open time r_(D) for the switchconnection D and possibly the open time t_(A) for the switch connectionA, for example in accordance with families of characteristicsintroduced, which take into account the efficiency on the one handmutual dependence of the volumetric flow and, the pressure available forthe hydrostatic drive 1 on the other hand. On basis of the desiredvalues entered via the input 37 for the volumetric flow and the meanhydraulic pressure detected in the pressure line 12 by a pressureindicator 38, the switch valve 3 can therefore be set via theclosed-cycled control device 36 so as to obtain an optimum control ofthe drive 1 for the specific case of use.

We claim:
 1. A device for controlling a hydrostatic drive comprising a resonator having a periodically actuatable switch valve which connects the resonator alternately with a pressurized-fluid supply line a return line and the hydrostatic drive, wherein the resonator (2) has at least one pressure chamber (6) with a movable, oscillatable chamber limitation (7) for changing the chamber volume; the movable chamber limitation (7) forms a part of a single-mass oscillator comprising mass and spring (10), and the pressure chamber (6) which is connectable alternately to the pressurized-fluid supply line (4), the return line (5), and the hydrostatic drive (1) via the switch valve (3) with a switch frequency which lies within the supraresonance region of the single-mass oscillator.
 2. A device according to claim 1, wherein the switch frequency of the switch valve (3) is adjustable.
 3. A device according to claim 2, wherein an open time (t_(D)) of the switch valve (3) for the connection of the pressure chamber (6) to the pressurized-fluid supply line (4) is adjustable.
 4. A device according to claim 2, wherein an open time (t_(D)) of the switch valve (3) for the connection of the pressure chamber (6) to the hydrostatic drive (1) is adjustable.
 5. A device according to claim 1, wherein the connecting line (12) between the pressure chamber (6) and the hydrostatic drive (1) is connected to a pressure accumulator (13).
 6. A device according to claim 1, wherein the pressure chamber (6) of the resonator (2) is formed as a cylinder (8), a piston (9) forms the movable chamber limitation (7) forming the single-mass oscillator having at least one said spring (10) acting on the piston (9).
 7. A device according to claim 6, wherein the resonator (2) is formed as said cylinder (8) divided into two chambers by said piston (9), each of the two pressure chambers (6) are connected via one of two switch valves (3) shifted 180° in phase with respect to their shift periods, each one of said two switch valves being connected to the pressurized-fluid supply line (4), the return line (5) and the hydrostatic drive (1).
 8. A device according to claim 1, wherein the movable chamber limitation (7) of the pressure chamber (6) of the resonator (2) comprises a bellows or a membrane (14).
 9. A device according to claim 1, wherein the switch valve (3) is formed as a rotary piston valve having a rotary piston (17) which connects the at least one pressure chamber (6) via control ports (21, 22, 23) alternately with connecting chambers (24, 25, 26) connected with the pressurized-fluid supply line (4), the return line (5), and the connecting line (12) for the hydrostatic drive (1).
 10. A device according to claim 9, wherein control bodies, which are coaxial to the rotary piston (17), are rotatably displaceable with respect to the pressure chamber (6), said control bodies forming control edges (32, 33, 34) cooperating with the control ports (21, 22, 23) of the rotary piston (17).
 11. A device according to claim 1 wherein an open time (t_(D)) of the switch valve (3) for the connection of the pressure chamber (6) to the pressurized-fluid supply line (4) is adjustable.
 12. A device according to claim 11, wherein an open time (t_(D)) of the switch valve (3) for the connection of the pressure chamber (6) to the hydrostatic drive (1) is adjustable.
 13. A device according to claim 1, wherein an open time (t_(D)) of the switch valve (3) for the connection of the pressure chamber (6) to the hydrostatic drive (1) is adjustable.
 14. A device according to claim 1, wherein an open time (t_(D)) of the switch valve (3) for the connection of the pressure chamber (6) to the hydrostatic drive (1) is adjustable.
 15. A device according to claim 1, wherein the switch valve (3) is formed as a rotary piston valve having a rotary piston (17) which connects a plurality of the pressure chambers (6) via control ports (21, 22, 23) alternately with connecting chambers (24, 25, 26) connected with the pressurized-fluid supply line (4), the return line (5), and the connecting line (12) for the hydrostatic drive (1).
 16. A device according to claim 15, wherein control bodies, which are coaxial to the rotary piston (17), are rotatably displaceable with respect to the plurality of pressure chambers (6) arranged with rotational symmetry to the rotary piston (17), said control bodies forming control edges (32, 33, 34) cooperating with the control ports (21, 22, 23) of the rotary piston (17). 